The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 22 390.4, filed on May 14, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a manufacturing process for a gravure paper with a maximal roughness depth of approximately 1.40 xcexcm (measured with the xe2x80x9cParker Print Surfxe2x80x9d method according to DIN-ISO 8791-4). The invention also relates to a gravure paper which is manufactured in a single work cycle.
2. Discussion of Background Information
Different printing processes are known from the prior art which place different demands on the quality and properties of the paper to be printed in order to achieve an optimal printing quality. In the gravure process, it is particularly crucial that the surface of the paper used is very smooth or has a very low roughness depth so that a sufficient printing quality is achieved, Furthermore, the porosity must be low in order to assure an optimal color absorption. In order to achieve the best printing quality, the sheet must also have a certain compressibility after being subjected to calendering.
In addition to the low roughness depth, however, a high tensile strength is also required in order to prevent tearing of the paper web during the printing process.
In order to produce a very high surface quality, i.e., a low roughness depth of the paper, the filler content or the pigment content of the fibrous material suspension must be kept as high as possible. This is because these very fine materials produce a very smooth and homogeneous surface of the paper. In addition. a fibrous material is used which has as high a beating degree as possible in order to produce a homogeneous sheet texture by utilizing the high content of fines. The uniformity and closed nature of the paper surface are of particular significance.
However, a high filler content runs counter to the requirement for a high strength of the paper. In order to achieve a high tear strength, an excessive filler content is not desirable since the filler acts as an obstacle to the hydrogen bridge formation between the fibers of the paper. In addition, a high beating degree impairs the strength due to a fiber-shortening effect.
Currently, in order to circumvent these opposing interests, gravure paper is in part manufactured so that coating-base paper is produced as a highly tear-resistant paper whose surface is coated with pigment and filler material in order to obtain a sufficient surface quality. However, this requires a high investment outlay because, in addition to the paper machine required for producing the paper, an investment must also be made in a coating machine, which may function either on-line or off-line in relation to the paper manufacturing process.
If one pursues the other possibility of keeping the beating degree of the paper as high as possible, i.e., in the vicinity less than approximately 40 ml CSF (Canadian Standard Freeness, see TAPI 227), and working with a relatively high total filler content, then this involves a powerful beating of the fibrous material. However, this is very energy intensive since the energy used rises exponentially as the beating degree increases.
The beating degree of fibrous material is frequently expressed in milliliters as Canadian Standard Freeness (CSF). In this connection, a high beating degree, i.e., a high fineness of the fibrous material or a high drainage resistance, corresponds to a low CSF value, whereas a lower beating degree corresponds to a high CSF value or a low drainage resistance.
The Applicant""s German Patent Application 196 24 127 A1, the disclosure of which is expressly incorporated by reference in its entirety, discloses a process for manufacturing a paper web with the aid of a multi-layer headbox. With this process for manufacturing a multi-layer fibrous material web, a headbox supplies a number of fibrous suspension streams to a web forming device in which, in order to produce a three-layer fibrous material web, the two outer layers are produced by utilizing two fibrous suspension streams whose composition is selected so that each outer layer is subsequently easier to drain than the inner layer, which is produced by providing a fibrous suspension stream with a correspondingly different composition. However, the specific information relating to the composition of the individual fibrous suspension flows is not given in this document.
Furthermore, the international application PCT/US97/01975 has disclosed applying uncooked starch to the surface of a fibrous material web which is still wet. This is performed in the vicinity of the wet section of a paper machine in order to improve the surface of the paper. However, no indication is given in this document as to the manufacture of a gravure paper.
The invention is therefore provides for a manufacturing process for gravure papers which is distinguished by a significantly more favorable energy expense and fibrous material utilization as well as a lower investment requirement than is customary in the prior art, The invention also provides for a gravure paper which, as a result of its manufacturing process, is less expensive to produce than in the prior art.
The invention recognizes that it is possible to produce a gravure paper by using a fibrous material that has a low beating degree with values of greater than approximately 50 ml CSF, preferably between approximately 50 ml and approximately 120 ml CSF, without having to use a coating machine in either an xe2x80x9con-linexe2x80x9d or xe2x80x9coff-linexe2x80x9d operation. Moreover, it is possible to situate the majority of the filler or pigment content of the finished paper web in the immediate vicinity of the surface of the finished paper web, such that, on the one hand, the tear strength of the gravure paper produced is increased and, on the other hand, the maximal surface roughness depth of the paper is not impaired. At the same time, however, the manufacturing process also takes place in one work cycle. In this connection, it is important for the dry matter content of the fibrous material web on which the filler and/or the pigment is deposited to be approximately xe2x89xa690%, preferably between approximately 3% to approximately 55%, and most preferably between approximately 5% to approximately 20%, since only in this way can a favorable bonding of the filler or the pigment to the fibrous material web be achieved.
With a constant basis weight, a high total filler content requires a lower relative content of strength-inducing fibrous material components. As a result, it is necessary to use higher quality and therefore more expensive fibrous material components. This disadvantage is prevented through the invention by the deliberate application of pigments to the surface of the paper. Consequently, more reasonably priced fibrous materials can be used without loss of quality.
According to one aspect of the invention, there is provided a process for manufacturing gravure paper with a maximal roughness depth of approximately 1.40 xcexcm which includes producing a stock suspension that has a stock with a freeness (i.e., measure for the beating degree) of greater than or equal to approximately 50 ml CSF (i.e., Canadian Standard Freeness), preferably between approximately 50 ml to approximately 120 ml CSF, and most preferably between approximately 50 ml to approximately 80 ml CSF, producing a fibrous material web using this stock suspension with the aid of a forming system, a first press section, and a drying section, applying at least one pigment and/or filler slurry to the unfinished fibrous material web in the vicinity between the beginning of the forming and a position at which a dry matter content of the fibrous material web is approximately xe2x89xa690%, and preferably between approximately 3% and approximately 50%, with the fibrous material content in the pigment and/or filler slurry preferably lying in the range from approximately 2% to approximately 60%, and preferably between approximately 5% to approximately 30%, such that no subsequent coating of the paper web is required.
This advantageously provides that the filler content is essentially concentrated in the layers that are close to the surface or that constitute the surface, since these layers are important for printing. This also allows for a low filler content in the center of the sheet, which contributes to the favorable tear strength of the paper, such that, by utilizing the additional reduction of the beating degree in comparison to the prior art to a beating degree of greater than approximately 50 ml CSF, an increase in the tear strength of the paper is also achieved. This also leads to the web attaining better runability through the paper machine and thereafter also through a printing machine.
An advantageous embodiment of the manufacturing process provides that after the at least one application of pigment and/or filler slurry, a passage through a press occurs. This passage through a press increases the bonding of the pigment and/or the filler coating to the fibrous material web.
According to the invention, the manufacturing process can be used on one side of the fibrous material web as well as on both sides of the fibrous material web so that the pigment and/or filler slurry can also be deposited on both sides of the fibrous material web.
There are a number of possible locations for the application of the pigment and/or filler slurry layer. These can include, for example, the forming system of the paper machine or the press section.
Because of the composition of the pigment and/or filler slurry, there is also the possibility of applying this to the fibrous material web through a wire. This advantageously allows the coating to be applied to the paper web at a time at which the tear strength of the paper web itself is not yet sufficient to remove it from the wire. Even if this were possible, the coating process would have a straining action on the fiber structure and would impair the later tear strength of the paper web. The application of the pigment and/or filler slurry can also take place through a wire and onto a paper web which is already relatively tear-resistant in order to reduce the potential of a possible web tear in the manufacturing process and therefore in order to increase the effective running time of the paper machine.
Advantageous values for the total coating weight of the at least one coating of the pigment and/or filler slurry on each side of the paper web is a moisture-free weight of from approximately 0.5 to approximately 10.0 g/m2, and preferably from approximately 1.0 to approximately 10 g/m2.
The manufacturing process is not solely limited to the application of a filler and/or pigment slurry to an already existing fibrous material web, but the gravure paper can also be produced according to the invention with a maximal surface roughness depth of approximately 1.40 xcexcm by virtue of the fact that a stock suspension is produced which has a fibrous material with a freeness (i.e., measure for the beating degree) of greater than or equal to approximately 50 ml CSF, preferably between approximately 50 ml to approximately 120 ml CSF, and most preferably between approximately 50 ml to approximately 80 ml CSF, simultaneously a filler and/or pigment suspension is produced, with the fibrous material/fines content in the pigment and/or filler suspension preferably lying in the range of between approximately 10% to approximately 95%, and preferably between approximately 30% to approximately 60%. Then, a fibrous material web is formed with the aid of a headbox which has at least two, and preferably at least three layers, with at least one layer, and preferably the two outer layers, being loaded with the filler and/or pigment suspension and at least one layer, preferably the inner layer, being loaded with the stock suspension described above. Then comes the formation of a paper web with the aid of a forming system, a press section, and a drying section, such that no subsequent coating of the paper web is required.
This process according to the invention also achieves the fact that in the outer layer to be printed or in the two outer layers, there is a very high filler and/or pigment content while, in the one fiber-containing layer, or in the inner layer, there are fibers with a relatively low beating degree that corresponds to greater than approximately 50 ml CSF, and preferably in the range from approximately 50 ml to approximately 100 ml CSF, so that a very favorable tear strength of the paper web is assured here.
For example, the following can be used as pigment or filler: kaolin, clay, powdered CaCO3, PCC (i.e., precipitated CaCO3), TiO2, talcum, bentonite.
In addition to these fillers or pigments, at least one of the following substances can be added: retention agents, dispersion agents, fixing agents, sizing agents, bonding agents, and starch. In addition, fines suspension can also be used.
Furthermore, the invention provides for a gravure paper with a surface roughness depth of approximately 1.40 xcexcm, which is manufactured by the following manufacturing process: producing a stock suspension that has a stock with a freeness of greater than or equal to approximately 50 ml CSF, preferably between approximately 50 ml to approximately 120 ml CSF, and most preferably between approximately 50 ml to approximately 80 ml CSF, producing a fibrous material web using this stock suspension with the aid of a forming system, a first press section, and a drying section, applying a pigment and/or filler slurry to the unfinished fibrous material web in the vicinity between the beginning of the forming and a position at which a dry matter content of the fibrous material web is approximately xe2x89xa690%, and preferably between approximately 5% and approximately 20% on at least one side of the web, with the fibrous material content in the pigment and/or filler slurry preferably lying in the range from approximately 2% to approximately 60%, and preferably between approximately 5% to approximately 30%, such that no subsequent coating of the paper web is required.
On the one hand, gravure paper manufactured in this way fulfills the requirement for a very favorable printability by utilizing the high filler content in at least one or also in both of the outer layers, and on the other hand, has a very closed, homogeneous, and flat surface. Furthermore, the runability of such a gravure paper is advantageously improved to a significant degree, such that, at the same time, due to the low beating degree required, a considerable energy savings is achieved in the manufacture of the stock used and therefore of the fibrous suspension. The gravure paper has particularly favorable properties if, after the application of the pigment and/or filler slurry onto the unfinished web, a passage through a press occurs, since a high degree of bonding of the pigment and/or filler layer to the fibrous material web is achieved thereby.
According to the invention, the gravure paper can be manufactured by virtue of the fact that the application of the pigment and/or filler slurry takes place in the forming system of the paper machine or in the press section of the paper machine.
The application of pigment and/or filler slurry onto the unfinished fibrous material web can also take place through a wire.
Advantageously, the total coating weight of the pigment and/or filler slurry on one side is from approximately 0.5 to approximately 10.0 g/m2, and preferably from approximately 1.0 to approximately 10 g/m2 in moisture-free weight.
The invention also proposes a gravure paper which has a surface roughness depth of approximately 1.40 xcexcm, which has been produced using the following manufacturing process; producing a stock suspension that has a stock with a freeness of greater than or equal to approximately 50 ml CSF, preferably between approximately 50 ml to approximately 120 ml CSF, and most preferably between approximately 50 ml to approximately 80 ml CSF, producing a filler and/or pigment suspension, with the fibrous material/fines content in the pigment and/or filler suspension preferably lying in the range from approximately 2% to approximately 60%, and preferably between approximately 5% to approximately 30%, producing a fibrous material web with the aid of a headbox that has at least two, preferably at least three layers, with one layer, preferably the two outer layers, being loaded with the pigment suspension and at least one layer, preferably the inner layer, being loaded with the stock suspension mentioned above, subsequently forming a paper web with the aid of a forming system, a press section, and a drying section, such that a subsequent coating of the paper web is not required.
The advantage of a gravure paper produced in this manner lies essentially in the extraordinarily more favorable energy requirement in the manufacture of the fibrous material suspension and an outstanding printability of the paper surface due to its high filler content. Since the investment in an additional coating machine can be eliminated, this is a very cost-effective manufacturing possibility.
With both the latter and the former gravure paper, at least one of the following substances can be used as pigment or filler. kaolin, clay, powdered CaCO31 PCC, TiO2 talcum, or bentonite. In addition, chemical supplementary agents, in particular bonding agents, can also be added in order to further improve the paper surface produced. Additional fines-containing suspension can also be added in order to increase the bonding forces.
The features of the invention which are mentioned above and to be explained below can be used not only in the combinations indicated, but also in other combinations or by themselves without departing the scope of the invention.
Additional features and advantages of the invention can be found in the following description of preferred exemplary embodiments with reference to the drawings.
According to one aspect of the invention, there is provided a method of manufacturing gravure paper having a maximal roughness depth of approximately 1.40 xcexcm in a paper machine comprising a forming system, a first press section, and a drying section, the method comprising producing a stock suspension comprising a stock having a freeness of greater than or equal to approximately 50 ml CSF, forming an unfinished fibrous material web from the stock suspension, and applying at least one of a pigment and a filler slurry to the unfinished fibrous material web between a beginning of the forming system and a position at which the dry matter content of the unfinished fibrous material web is approximately xe2x89xa690%. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 120 ml CSF. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 80 ml CSF. After the applying of the at least one of the pigment and the filler, no subsequent coating may occur. A fibrous material content in at least one of the pigment and the filler slurry may be in the range of between approximately 2% to approximately 60%. The fibrous material content in the at least one of the pigment and the filler slurry may be in the range of between approximately 5% to approximately 30%. The gravure paper may be manufactured without utilizing coating which does not occur in at least one of the forming system, the press section, and the drying section. The applying may occur before the unfinished fibrous material web passes through the press section of the paper machine. The applying may occur before the unfinished fibrous material web passes through the press section and the drying section of the paper machine. The applying may further comprise applying at least one of the pigment and the filler on both sides of the unfinished fibrous material web.
The applying may occur in the forming system of the paper machine. The applying of the at least one of the pigment and the filler slurry to the unfinished fibrous material web may occur in the press section of the paper machine. The applying may occur when the unfinished fibrous material web has a dry matter content of less than approximately 55% The applying may occur when the dry matter content is between approximately 3% to approximately 55%. The applying may be performed through a wire.
A total coating weight of at least one application of one of the at least one of the pigment and the filler slurry on one side of the unfinished fibrous material web may comprise a moisture-free weight of between approximately 0.5 to approximately 10.0 g/m2. The moisture-free weight may be between approximately 1.0 to approximately 10 g/m2.
The invention also provides for a method of manufacturing gravure paper having a maximal roughness depth of approximately 1.40 xcexcm in a paper machine comprising a forming system having a headbox, a first press section, and a drying section, the method comprising producing a stock suspension comprising a stock having a freeness of greater than or equal to approximately 50 ml CSF, producing a coating suspension comprising at least one of a filler and a pigment, the coating suspension having a fiber content in the range of between approximately 10% to approximately 95%, forming a fibrous material web comprising at least two layers with the headbox, wherein at least one layer is formed from the coating suspension and another layer is formed from the stock suspension, and forming a paper web by guiding the fibrous material web through the forming system, the first press section, and the drying section. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 120 ml CSF. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 80 ml CSF. The fiber content may be in the range of between approximately 20% to approximately 60%. The at least one of the pigment and the filler may comprise at least one of kaolin, clay, powdered CaCO3, PCC, TiO2, talcum, and bentonite. The at least one of the pigment and the filler may comprise at least one of retention agents, fixing agents, dispersion agents, sizing agents, bonding agents, and fines suspension, The at least one of the pigment and the filler may comprise at least one of retention agents, fixing agents, dispersion agents, sizing agents, bonding agents, and fines suspension.
The invention also provides for a gravure paper having a maximal surface roughness depth of 1.40 xcexcm which is made in a paper machine comprising a forming system, a first press section, and a drying section by a method comprising producing a stock suspension comprising a stock having a freeness of greater than or equal to approximately 50 ml CSF, forming an unfinished fibrous material web from the stock suspension, and applying at least one of a pigment and a filler slurry to the unfinished fibrous material web between a beginning of the forming system and a position at which the dry matter content of the unfinished fibrous material web is approximately 90%. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 120 ml CSF. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 80 ml CSF. After the applying of the at least one of the pigment and the filler, no subsequent coating may occur. A fibrous material content in the at least one of the pigment and the filler slurry may be in the range of between approximately 2% to approximately 60%. The fibrous material content in the at least one of the pigment and the filler slurry may be in the range of between approximately 5% to approximately 30%. The gravure paper may be manufactured without utilizing coating which does not occur in at least one of the forming system, the press section, and the drying section. The applying may further comprise applying at least one of the pigment and the filler on both sides of the unfinished fibrous material web.
The applying may occur before the unfinished fibrous material web passes through the press section of the paper machine. The applying may occur before the unfinished fibrous material web passes through the press section and the drying section of the paper machine. The applying may further comprise simultaneously applying at least one of the pigment and the filler on both sides of the unfinished fibrous material web. The applying may occur in the forming system of the paper machine. The applying of the at least one of the pigment and the filler slurry to the unfinished fibrous material web may occur in the press section of the paper machine. The applying may occur when the unfinished fibrous material web has a dry matter content of less than approximately 55%. The applying may be performed through a wire.
A total coating weight of at least one application of one of the at least one of the pigment and the filler slurry on one side of the unfinished fibrous material web may comprises a moisture-free weight of between approximately 0.5 to approximately 10.0 g/m2. The moisture-free weight may be between approximately 1.0 to approximately 10.0 g/m2.
The invention also includes a gravure paper having a maximal surface roughness depth of 1.40 xcexcm which is made in a paper machine comprising a forming system having a headbox, a first press section, and a drying section by a method comprising producing a stock suspension comprising a stock having a freeness of greater than or equal to approximately 50 ml CSF, producing a coating suspension comprising at least one of a filler and a pigment, the coating suspension having a fiber content in the range of between approximately 2% to approximately 60%, forming a fibrous material web comprising at least two layers with the headbox, wherein at least one layer is formed from the coating suspension and another layer is formed from the stock suspension, and forming a paper web by guiding the fibrous material web through the forming system, the first press section, and the drying section, The stock suspension may comprises a stock having a freeness of between approximately 50 ml to approximately 120 ml CSF. The stock suspension may comprise a stock having a freeness of between approximately 50 ml to approximately 80 ml CSF. The fiber content may be in the range of between approximately 5% to approximately 30%. The at least one of the pigment and the filler may comprises at least one of kaolin, clay, powdered CaCO3, PCC, TiO2, talcum, and bentonite. The at least one of the pigment and the filler may comprise at least one of retention agents, fixing agents, dispersion agents, sizing agents, bonding agents, and fines suspension. The at least one of the pigment and the filler may comprise at least one of retention agents, fixing agents, dispersion agents, sizing agents, bonding agents, and fines suspension. The coating suspension may comprises a stock having a freeness degree of approximately xe2x89xa630 ml CSF. The freeness degree may be approximately xe2x89xa620 ml CSF. The fiber content of the coating suspension may be between approximately 50% to approximately 100% less than a fiber content of the stock suspension.